Return of the Heavenly Demon King
by xAstrea
Summary: Ishikawa never expected any of this to happen, that is until one day something happened in the park which escalated a non-stop chain of events which always seemed to involve her in them. Fem!Issei, !SlightAU.
1. Chapter 1

**Prologue –** A Violent Awakening

 _Riiiiiingggg!_

A figure on the bed stirred, before raising a hand to slap the offending device on the table, effectively silencing it.

' _Sigh. Another long day of school.'_ Ishikawa thought to herself.

Getting herself off the bed, she slowly made her way towards the bathroom with the efficiency of a half awake sloth, almost tripping over her kotatsu on her way.

After spending fifteen minutes washing and freshening up, Ishikawa stood in front of the mirror and took in her appearance.

What greeted her was an image of a typical female 17 year-old high school student with her long black hair. Bright vermillion eyes coupled with a decently attractive face gave her the beauty to stand out from the other girls of her age. The most attention grabbing part of her weren't her brilliant eyes, not her beautiful looks but a vertical scar that ran across her left eye. Subconsciously raising a hand, she touched the scar, remembering the incident that caused her the injury and how it had changed her life forever…

 _Flashback: Seven years prior._

"Did you enjoy the movie, my dear?"

Asked Hyoudou Misa as the family of three walked down the now empty streets of Kuoh towards their home, just having caught a late night movie ending at midnight.

"Yeah! The main character was so cool!" exclaimed a ten year old Ishikawa with bright eyes.

Seeing their daughter's megawatt smile, Ishikawa's parents both laughed as they ruffled her hair.

"Since it's already this late, why not we take a small detour to the scenic route through Kuoh City Park?" suggested Hyoudou Gorou as they passed by the East park entrance.

"Okay!" cut in Ishikawa before her mother had any say in the matter, her disapproving frown already in place.

As they strolled through the park, Ishikawa's parents noticed the atmosphere turn quiet and still.

"We should leave dear." Misa whispered urgently to her husband.

"Indeed, this does not feel right."

Just as the family turned around, an almost too cheerful female voice called out to them from the side.

"Ara? What do we have here? A bunch of humans who wandered somewhere they shouldn't have?"

Turning around, the stunned family saw a young girl with purple hair dressed in school uniform. It would have been nothing alerting if not for the two dead bodies at her feet, an European longsword in her hands still dripping with fresh blood, and a pair of jet black wings as dark as the night sky hanging behind her.

"What's wrong? Cat got your tongue? Never seen a Fallen Angel before? Regrettably I have to end you where you stand. Can't leave witnesses behind see?" said the Fallen as she started walking at a sedate pace towards the family, with eyes like those of a predator playing with its prey.

"Ishi, run." stated Gorou, his tone leaving no room for argument as he got into a martial arts stance alongside his wife, which only seemed to amuse the Fallen.

Choking back a sob, Ishikawa ran in the direction of the neighbourhood police post, ignoring the screams and grunts of her parents and the sadistic laughter of a girl. Before she managed to even get far, the Fallen Angel landed right in front of her, tossing the decapitated head of her father and mother at her feet. Startled, Ishikawa fell backwards and onto the floor, face full of tears.

"Thinking about running are we? Don't worry, you will soon join your parents in the depths of Hell."

Looking at the screaming heads of her parents, she saw _red_.

 _Anger._

Ishikawa felt her head hurt, as memories that are not hers began to flood her mind. Memories of burnt bodies and severed heads not unlike her parents and a once glorious temple ablaze, burning to the ground. A beautiful sight.

 _Burn. Incinerate. DIE._

Despite her fear, intense anger took over and gave her strength as she glared at the Fallen as she knelt beside the heads of her parents.

"Oooh I like those eyes kid, red like a burning inferno, full of desire and hate. But what can you do? A mere human can't even stop me, let alone a human kid. No matter, you will be dead in a moment anyway." gloated the Fallen as she lazily swung at Ishikawa.

Her first, and most fatal mistake.

The Fallen glanced on with incomprehension as the burning stump that used to be her right hand was gone in an instant, incinerated by purple flames. Before she could regain her bearings, she was punched in the gut, _real hard,_ and was thrown onto her back.

"How dare yo-! Arghh!"

Ishikawa had moved toward the screaming Angel with a speed that surprised herself and impaled her remaining hand to the ground with her own sword before she could finish her sentence, pinning her to the ground.

The Fallen took a good look at the kid before her for the first time after regaining her bearings.

"Not so smug now are y- Nngh!"

The Fallen had gathered light energy into a makeshift blade using one of her legs and kicked it upwards as she was speaking, scraping Ishikawa's left eye causing temporary blindness. Pushing her remaining hand all the way up the length of the sword and grasped the guard, pulling it out and letting it fall aside to the ground.

Summoning another proper crimson light spear in her hands this time, with all light of playfulness gone, she gave Ishikawa a hateful glare, a glare that promised unspoken depths of pain as she lifted herself into the night sky, wings spread out behind her.

"You will pay dearly for my arm. You will remember the wrath of Lucretia! Your newly awakened Sacred Gear won't save you from the pain you will face, who have never seen combat before today!"

The Fallen Angel now identified as Lucretia cocked her arm back and channelled all of her remaining energy into the spear before throwing it, spear tip soaring straight at Ishikawa's heart at speeds rivalling a bullet fired from a high-caliber rifle.

The only thing that saved Ishikawa was her new powers as the purple flames, as if on reflex they manifested from the ground, forming a temporary transient purple wall right in front of her before the spear could gouge her heart out. During the time the two powers were clashing, a beautiful red Japanese katana appeared and absorbed both energies and released a white hot aura of flame. Strangely, the flames didn't seem to bother her.

The katana then guided itself into Ishikawa's hands and slashed at Lucretia, unleashing the stored energies straight at the Fallen in the form of a burning Phoenix with the intent of razing everything in its path.

The Fallen Lucretia could only stare on in disbelief at her pending doom, lamenting that she was bested by a mere child, before the flames consumed her every bit of existence, wiping her off the face of the earth and continued into the night sky, momentarily illuminating the world in a flash fire rivalling the sun.

With the Fallen gone, Ishikawa felt her knees buckle as her strength left her. Kneeling before the remains of her parents, she wept as she remembered the last ten years of her peaceful life.

' _Father… Mother…I have avenged you.'_

And then her world went black.

* * *

 **Hey everyone, sorry for the really long inactivity.**

 **I will not give any excuses, but long story short? Writer's Block and College.**

 **I have tried to continue Chapter 3 but realised that I had dug myself into a hole with my poor planning, making shit up on the fly and hasty updates for Chapter 1 and 2.**

 **I have decided to rewrite this story by setting a proper backstory for the MC and having plans on how the story will progress.**

 **Once again I am very sorry that it took a whole year for me to update.**


	2. Chapter 2

**Chapter I** – Aftermath

Ishikawa was floating, or at least she thought she was.

As her senses returned to her, the first thing she felt was the comfort of a bed.

' _Where… am I…?'_ pondered Ishikawa as she took in her surroundings.

She was in a standard isolated hospital bedroom. Her left eye was covered by a roll of bandage so her window of vision was halved. The windows were shut with a blind. A vase of flowers was placed on the table in front of her bed. The atmosphere had a faint citrus scent.

Before she could fully comprehend her current situation regarding the night before, she heard the sound of the door knob twisting and in came a man in his twenties wearing a business suit. His hair was the shade of onyx except for his golden blonde bangs. A neatly trimmed black goatee framed his sharp chin, giving him an overall appearance of a salaryman.

At his sight, Ishikawa unconsciously sat up straighter.

"Ah it seems like you are awake." the man said as he walked towards the foot of her bed. "Do you recall what happened the night before?"

At his words, memories of the events which transpired the previous night began to flood into Ishikawa's mind. Everything from the Fallen encounter to Ishikawa's awakening, her injury, the death of the Fallen and most importantly, the death of her parents.

' _Mom… Dad...'_

At the memory of their silently screaming severed heads laying at her feet, Ishikawa began to tear up. Unable to handle the sudden surge of emotion that burst forth from the depths her heart that she repressed, she broke down crying.

The man, having seen countless cases like this in his long life, wordlessly stood by her, pulling her into a silent hug as she cried into his chest.

It took Ishikawa ten minutes to calm down from her sobbing fit.

"Are you feeling better?" Inquired the man.

Not trusting her voice, Ishikawa gave a small nod as she looked up at her supposed saviour.

"Well kiddo, allow me to answer all the unspoken questions I can see in your eyes" began the man. "Firstly, I believe introductions are in order. My name is Azazel, Governor General of the Fallen Angels of Grigori and you are currently in the medical ward of our Kuoh Outpost."

At the mention of the Fallen, Ishikawa's eyes widened before unconsciously sinking further into the bed, pulling her blanket over her face.

"Before you panic, the Fallen who attacked you last night was regrettably a rogue member. I assure you that I, and the rest of the Grigori mean you no harm." Reasoned the Governor.

"Now onto more pressing matters, I believe you know next to nothing about the Moonlit World?"

At the sight of another nod, Azazel only sighed before continuing.

"I won't bore you with the history lesson, so here's the main gist of things. There are the Three Biblical Factions, the Angels of Heaven, Devils of the Underworld, and us, the outcasts of Heaven, Grigori."

Pausing to let the information sink in, he continued.

"After the Great War which occurred roughly 800 years ago, the three factions made an unofficial peace and things toned down. But right now things are so tense that a smallest spark could cause yet another Great War.

"Of course, I want nothing more than true peace. However there are some of my people who miss the glory days of battle, wishing for nothing more than to bask in the thrill of total war. In fact, one of Grigori's leaders by the name of Kokabiel and his army have gone rogue. The one you faced, Lucretia, was one of the many Fallen under his command. That is why I am gathering people who I know are trustworthy to squash out the rogue fallen.

"We found you collapsed next to the fountain in Kuoh Park, there were no traces of Lucretia except for her faint excess magical signature. With your parents gone, the Japanese Government will seize your household and you have nowhere left to go except for the Orphanage. But considering your newly awakened Sacred Gear, I am willing to take you in and give you shelter and protection, at the same time training you to become one of my agents. Oh, and I do happen to be quite the Sacred Gear expert. So, what do you say kiddo?"

* * *

 _Present day_.

Seven years went by quickly.

After Ishikawa accepted Azazel's offer she was brought to their main branch in Europe and given shelter from the other Supernatural factions as promised. She was also trained in the arts of espionage. Everything from infiltration to combat skills to even improving her own Sacred Gear control.

Before long, she had risen up among the ranks of the Grigori agents and gained the respect of most of the Fallen under Azazel's leadership, quickly earning her the title of "Fallen Executor".

Throughout her stay at the Grigori, Azazel had taken time off his busy schedule as Governor to check in on her from time to time, bringing with him gifts around the world from his travels. She had grown to see Azazel as a father figure.

Moving her hand down to touch the small necklace in the shape of a golden cross with four purple gems. This is Ishikawa's Sacred Gear, Incinerate Anthem in standby form.

 **[Oouii sleepyhead! How long do you plan on staring at yourself?]** spoke a female voice in her head, originating from said necklace.

It also happens to house the soul of one Japan's female warlords, Oda Nobunaga.

Yes, _female_ warlord.

Ishikawa herself was also shocked to find out how wrong history was at portraying one of the most prominent figures of Japan as a man. However, with both of them sharing similar views, they hit off pretty well and became partners rather quickly.

Ishikawa took the next thirty minutes to shower and dry her hair, tying it up in a high ponytail before dressing herself up in her new Kuoh Academy uniform. She finally returned to Kuoh after seven years away with the Grigori's main base in Europe. Azazel had sent her back to Kuoh as the Grigori's representative to start diplomatic relations with the two heiresses in charge of the city, at the same time exterminating any rogue members of the Grigori in the city to prevent another Great War.

The Kuoh Academy student hostel Ishikawa was staying in is conveniently located one street away from the school itself and access to necessities like convenience stores and supermarkets with a short five minute walk. Unknown to the students unware of the supernatural, the hostel was also cover with magical barriers and the dorm leaders are two Middle-Class Devils from the Gremory and Sitri clans respectively.

As she walked towards her class, Ishikawa took her time to think about her mission which she had mixed feelings of. On one hand, she was eager to return to the city of her birth as it contained many memories of her ten years of childhood. Yet on the other hand, it was also within this city that took away the two most precious people in her life in one night. But then again, that was seven years ago.

 **[What, getting sentimental now? It's a little too late for that dontcha think?]** teased the resident Demon Archer.

She was right, those concerns could wait, right now she had a first impression to make.

"Okay class before we begin I have an announcement. We have a new transfer student from Europe."

"Oh! I bet it's a girl! I bet she'd be a real hottie!" came a certain perverted baldy.

"Tsk you and your perverted thoughts, I bet it's another prince like Kiba. Ahhnn~ How dreamy~" exclaimed one of the female students.

"Alright settle down, for now why don't you come on in?" said the teacher as he looked toward the door.

The door slid open and everyone's attention was drawn towards the entrance.

As Ishikawa strode into her class she heard a few gasps and whispers from her new classmates.

"Oooh I was right it's another beauty, you owe me 500 yen now Kiryuu." gloated the bald guy.

"Tsk you win this time perverted baldy." The bespectacled girl shot back.

The chatter died down once she wrote her name on the board, Ishikawa then turned to face the class and spoke.

"I am Hyoudou Ishikawa, pleased to meet all of you."

A moment of silence passed.

 **[Huh, that went pretty well.]**

And that was when, the class went wild.

"Hyoudou-san! Were you born in Europe?"

"Hyoudou? That's not an European name…"

"Hyoudou-san! Why don't you look European?"

"Hyoudou-san, what happened to your left eye?"

"Ishi-chan please marry me!"

 **[… Forget I said anything.]**

"Uhh... what?" Equally stunned, Ishikawa didn't know how to respond. It was the timely intervention of her homeroom teacher that saved her from the relentless bombardment of questions from her classmates.

"Alright class settle down, you can get to know her during break, for now Hyoudou-kun you may take that empty window seat at the back next to Aika-kun. Now let's begin our lesson, please turn to page 43 on Japan History."

The teacher went on to ramble about the history of Japan that Ishikawa was already intimately familiar with thanks to the soul of Nobunaga within her sacred gear.

Well, so much for a first impression.

*Riiiing!*

"Alright class we will stop here for today, remember to submit your thousand word essay on the Oda clan by Friday." Said the teacher as he left the classroom.

All students released a collective sigh of relieve that the boring lesson was finally over.

"Hey Miss Transfer Student do you want to eat with- Huh?" began Kiryuu as she realised that the seat next to her was empty. "Could've sworn she was sitting there a moment ago. What is she a ninja?"

As soon as she heard the bell, Ishikawa abused her infiltration training to escape the classroom with silence before any of her classmates could notice. Socialising can wait, she had more pressing matters to attend to.

She made her way to the old school building which housed the Occult Research Club to make first contact with the devils as per her mission briefing.

Before she could leave the main building however, she was approached by a male student with short blonde hair and grey eyes.

"Ah excuse me, Hyoudou-san. I am Saji Genshirou from class 1-C. I am here to invite you to the Student Council room on behalf of the Kaichou, Souna Shitori." said Saji with a small bow.

Giving him one eye over, gave a small nod and waved for him to lead the way.

Shitori huh, seems like the Sitri household's next heiress is smart enough to hide her identity under an alias, unlike the Gremory heiress.

"So… how are you enjoying your first day at school so far?" questioned Saji, hoping to dispel the awkward silence between them.

"So far? Not that bad, except that there was that one gloomy looking guy with spectacles staring at me from the other corner of the classroom… He sort of creeps me out honestly." she replied with a slight shiver.

"Ah you mean the one that is chummy with the baldy? That's Motohama… He and the baldy are infamously known as the Perverted Duo… as bad as that sounds they are actually really nice people deep down."

"Perverted Duo? What, do they go around harassing girls?"

"Um... pretty much? Except that they mostly go after the Kendo club anyway so you should be fine. Though by the way you said that perverted glasses was staring at you, he may have found a new target." Saji nervously replied, while neglecting to mention that Motohama was probably taking her three-sizes. If what he read about Ishikawa in the reports were true, he definitely did not want to gain her ire on her first day here. Especially not when knowing how Sona would punish him for wasting an opportunity to make potential allies. Hell hath no fury like a woman scorned, he valued his manhood after all.

"Oh goodie, first day of school and I've been targeted." she remarked sarcastically.

"Ah on the bright side though they only target beauties so it is technically a compliment?" Saji suggested with a small laugh.

"Right… If they do anything perverted to me though I am punching them through a wall, and I will not hold back even if they aren't dwellers of the Moonlit World." she said with narrowed eyes.

Swallowing nervously, Saji nodded as he opened the door to the Student Council room.

"After you." He motioned.

Stepping into the Student Council office, Ishikawa was greeted with the sight of a neatly arranged room. The walls were lined with photo frames of modern art. The wooden floors shined with a layer of varnish. To the left seated on the commons meeting table were three girls busy with sorting out stacks of documents. On the right was a guest corner, with a coffee table flanked with two really expensive looking sofas. A row of storage cabinets neatly lined the walls behind the sofas on the right. Finally, facing the door with a red carpet leading towards the entrance was the President's table. Behind the desk sat an immaculately dressed bespectacled girl with a short bob haircut. Despite wearing the same uniform as the rest of her peers, she somehow managed to outshine them with sheer tidiness. Her fingers were crossed in front of her face as her eyes were closed in deep thought. On her left stood another taller bespectacled girl with long flowing black hair with her hands in front of her like the president's personal assistant. Overall, it gave off an atmosphere of a cosy Victorian styled office. It was definitely not what Ishikawa expected as a base of operations for the Sitri heiress's peerage, she was after all, literally walking into the Devil's Den.

"Kaichou, I've brought the transfer student as asked." Called out Saji as he went to join the other three girls with sorting documents.

"Please, take a seat. Tsubaki, make some tea." Said Sona as she rose from her seat at the president's desk and motioned towards the guest's corner.

Wordlessly, the taller bespectacled girl moved to retrieve a tea set from one of the cabinets and began brewing tea.

"These are real comfortable sofas. You Devils sure know how to indulge in the finer things in life huh." Spoke Ishikawa as she sat into the sofa, crossing a leg over and making herself comfortable.

"Believe me, you have not seen how far Devils go to show their wealth if you think that this is all we are capable of." Countered Sona, "Let's get down to business. On behalf of the 72 Pillars, I, Sona Sitri formally welcome you, to Kuoh. I take it you are familiar with the city, seeing that you were a resident until 7 years ago."

At the sight of a nod from Ishikawa, Sona continued.

"While have indeed received reports of increased Fallen activity in Kuoh, but seeing that they are not causing any trouble here, I cannot help but be curious of the need for your presence here. Is there something we are being kept in the dark of?" She questioned.

Reaching into her bag, Ishikawa pulled out a document with 'Top Secret, for the eyes of Sona Sitri only.' stamped across the front and handed it to her.

"Here, a sign of goodwill from Azazel himself." She said with a small smirk.

Raising an eyebrow, Sona took the document and began to scan through its contents. Ishikawa took the moment to raise the teacup she was given by Tsubaki to her nose, taking a quick whiff of the fragrant aroma before taking a small sip, identifying its rich taste as Earl Grey tea. A rather expensive one to boot.

"I must say, this is real good tea. Thank you for such kind hospitalities." Complimented Ishikawa.

"You're welcome." Came a curt reply from Tsubaki.

It was at this moment that Sona finished reading the document, and she looked up with a slightly shocked expression, one rare coming from the stoic girl.

"You are telling me, a Ten-Winged Fallen, Kokabiel of the Bible no less, has gone rogue and is planning on something big, with Kuoh possibly being his next target?" She questioned with a raised eyebrow.

"At least, that is what we suspect. Kokabiel has been well known for manipulating his fellow Fallen into doing his bidding, by relaying orders 'from the Governor General himself'. We believe that the increased presence of Fallen here is no coincidence." Pausing to take another long sip of her tea, Ishikawa continued. "While we currently have no idea what exactly his plans are, we know that it is one that will affect the Supernatural world on a rather large scale judging from the extended period of silence on his part. Kokabiel was never one to lie low and would jump at any opportunity to re-ignite a second Great War. While I hope that this is not the case, it does not hurt to be on the safe side."

"Agreed, the last thing we want is another War on our hands. The Devils are still recovering from the Civil War between the Old and New Satan Factions. An all-out war between the Three Factions would be something we cannot afford. Very well, you have my permission to freely operate within Kuoh. Do let us know if we may be of any assistance, best of luck for your investigation. I would suggest heading over to the Old School building to speak to Rias Gremory as well, I will inform her of your arrival." concluded Sona as she stood up and stretched out her hand. "Here's to a lasting partnership and peace."

Staring at Sona's extended limb, Ishikawa stood up and firmly grasped her hand and shook it.

"For peace." She simply said.

* * *

 **Hey everyone, uh... its been awhile hasn't it?**

 **Hope you guys have enjoyed this small update.**

 **No excuses this time, I simply lost the motivation to write for a really long time. It was only because of all the positive reviews you guys have been giving that got me back into updating this story. My sincerest thanks for that.**

 **Once again, do leave a review as it would help me improve as a novice writer.**

 **I will see you guys on the next update.**


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